A relatively thin plane illumirnation device has been extensively used such as for a backlight of a liquid crystal display, an interior illuminator, a signboard, and other various types of displays.
One conventional illumination device comprises a light source for generating a strip of light like a fluorescent tube, and a radiation plate for diffusing the light coupled into one edge thereof and radiating the diffused light from the surface thereof. The first conventional illumination device, however, there is a disadvantage in that many factors, such as a dealing with heat generated by the fluorescent tube, a mechanical protection against the fluorescent tube, must be considered. Especially, since a high-luminescent light source which generated more heat value is easy to break and needs to be mechanically protected, it may not be applicable to an illumination in such a place as no electricity is preferable, or explosion-proof devices are required.
In order to overcome these shortcomings, a use of bundled optical fibers for guiding light from a light source to an edge of a radiation plate has been studied. The second conventional illumination device, however, requires an optical fiber cable having a substantially complicated structure comprising bundled optical fibers, one ends of which are bundled together and optically connected to a light source, and another ends of which are separated with each other and optically connected to one edge of a radiation plate at distributed positions along the edge. Therefore, there are disadvantage in that;
(a) a complicated optical fiber cable and complicated connections between the light source and the radiation plate are necessary. It makes the cost high. PA1 (b) a large space in which the bundled optical fibers are bent and connected to the radiation plate is necessary in the vicinity of interface. As a result, the illumination device becomes bigger and heavier, and a relatively large volume of the illumination device other than an illuminating plane makes it less aesthetic.